Operational comparison of various thermodynamic treatments of organic substance adsorption at the electrode/solution interface

Three isotherms are considered: Frumkin's Bennes' and Mohilner's. The relationship between the interaction parameters in the first two and the adsorbate activity coefficient in the last is discussed. The significance of various standard states for the definition of ΔG° _ads is analysed. The operational derivation of ΔG°_ads in the three cases and the relationship between the resulting three quantities are illustrated. The isotherms have been used to describe the adsorption of 1,4-dioxane on a polarized Hg electrode. The analysis has been carried out both at constant potential and constant charge. The picture emerging in each of the three cases is discussed in the light of the results obtained in the other two. It is concluded that the three approaches give the same qualitative information about the interfacial behaviour of dioxane, especially as far as the effect of the electric field and the particle-particle lateral interaction are concerned. The usefulness of the Frumkin isotherm for analysing promptly experimental adsorption data is thus maintained. Limitations of the present approach are discussed.     

A discussion on the energies involved in specific adsorption of ions

The change in specific adsorption of I^? ions on the series of metals Au, Hg, Bi, Pb, Cd, and Ga is analyzed using data of specifically adsorbed charge and shift in potential of zero charge. Factors determining the change in adsorbability are discussed in the light of previous formulations. It is shown that the work connected with water desorption as an ion becomes adsorbed, usually neglected or underestimated in previous discussions, is very likely to be the main factor determining the change in adsorbability along the series of metals. A rough estimation of energies involved in water desorption suggests that metal—water surface bonds are probably weak on sp-metals so that they are unable to affect the reactivity of metal surfaces with respect to the gas phase as strong covalent surface bonds are involved, for instance in the hydrogen evolution reaction. Conversely, the strong effect of water desorption on the specific adsorption of ions may be an indication of ion—metal interactions to be substantially independent of the nature of the metal. This suggests that covalent contributions to the surface bond are apparently minor for metals more electropositive than Au.     

Surfaces and Interfaces in Electrochemistry: 2003 Frumkin Memorial Medal Award Lecture

This Award Lecture, delivered on the occasion of the presentation of the 2003 Frumkin Memorial Medal to the Author, consists of three parts: A brief introduction, a memorial section where the events in which Professor Frumkin and the author were jointly involved, and a scientific section where the main concepts at the basis of the scientific contacts between Frumkin and the author are illustrated. Among the latter, emphasis is placed on the relationship between the potential of zero charge and the electron work function of metals.     

Oxygen evolution on aged IrO x /Ti electrodes in alkaline solutions

O₂ evolution from 1 mol dm⁻¹ NaOH aqueous solution was studied on IrO _x /Ti electrodes already used for more than 3 years (aged). IrO _x was prepared by thermal decomposition of the chloride in the temperature range from 330 to 500 °C. Half of the electrodes were stored in air between experiments, the other half in water. The state of the electrode surface was monitored by recording voltammetric curves in a potential region prior to O₂ evolution before and after each group of experiments. O₂ evolution was studied by measuring quasistationary current–potential curves. Tafel slopes were derived using two different approaches. The reaction order with respect to OH⁻ was also determined and found to be fractional. Results show that the reaction mechanism does not depend on either the calcination temperature or the storage conditions. However, stability appears to be higher for electrodes calcined at higher temperatures and stored in air. Dedicated to Professor Algirdas Vaškelis on the occasion of his 70th birthday.     

Effect of the nature of the metal on the dielectric properties of polar liquids at the interface with electrodes. A phenomenological approach

The dielectric behaviour of water, DMSO and ACN at the interface with transition and non-transition metals is examined by analysing the inner-layer capacity as a function of the metal surface chemical affinity. An, inner-layer capacity in the absence of metal-solvent specific interaction is defined and derived by graphical correlations. The permittivity of the surface phase of the solvent under these conditions is derived and analysed to elucidate the nature of the factors contributing to the dielectric behaviour at an interface. The capacity-potential curves for Fe, as a typical transition metal, are elaborated to investigate the orientation of the solvent on the surface and the applicability of the Gouy-Chapman-Stern model. Suggestions on the nature of the metal-water surface bond are given on the basis of the derived parameters. The structure of the double layer in ACN at transition metals is discussed in the light of recent measurements.     

Effect of Surface Structure on Behavior of RuO2 Electrodes in Sulfuric Acid Aqueous Solution

The electrochemical properties of RuO₂ electrodes are studied by means of cyclic voltammetry, potential step, and impedance measurements in aqueous 0.5 mol/dm³ H₂SO₄ as a supporting electrolyte solution and applying the hanging electrolyte meniscus technique. Two types of the electrodes are used: bulk as-grown single-crystal having (101) exposed interface and 500 nm film produced by reactive RF magnetron sputtering at 450°C. The surface structure of the RuO₂ electrodes prepared by different techniques is defined from X-ray LAUE backscattering. Experimental data show that, for both RuO₂ electrodes, the charging components include a slow diffusion-controlled contribution, due to proton injection–ejection. The diffusion characteristics and the diffusion coefficients for the same electrodes are estimated and reported.     

Measurement of the e+e-→π+π-π+π- cross section in the ϱ′(1600) energy region

The cross section for the reaction e⁺e^-→π⁺π^-π⁺π^- has been measured at the e⁺e^- storage ring Adone, in the to tal c.m. energy range 1.42–2.20 GeV. The peak and the following descent of the ?′(1600) resonance is observed. Using also lower energy data, and assuming that only one resonant amplitude contributes to the observed cross section, the parameters of the ?′(1600) are deduced.